Abstract

The detection limits for NO and NO2 in turbine exhausts by nonintrusive monitoring have to be improved. Multipass mode Fourier-transform infrared (FTIR) absorption spectrometry and use of a White mirror system were found from a sensitivity study with spectra simulations in the mid-infrared to be essential for the retrieval of NO2 abundances. A new White mirror system with a parallel infrared beam was developed and tested successfully with a commercial FTIR spectrometer in different turbine test beds. The minimum detection limits for a typical turbine plume of 50 cm in diameter are approximately 6 parts per million (ppm) for NO and 9 ppm for NO2 (as well 100 ppm for CO2 and 4 ppm for CO).

Figures (16)

Optical depths of NO2 and interfering compounds (CO2 and H2O) in the spectral region 1595–1605 cm−1 for the power setting NH of 65%. The absorption signatures for 32 passes of single gases as well as of the gas mixture (sum) are given.

Transmissions of NO2 together with H2O and CO2 in the spectral region 1595–1605 cm−1 for the power setting NH of 65%. The absorption signatures for single pass (total transmission) as well as for 16 and 32 passes are given.

Optical depths of NO2 and interfering compounds (CO2 and H2O) in the spectral region 1627–1637 cm−1 for the power setting NH of 65%. The absorption signatures for 32 passes of single gases as well as of the gas mixture (sum) are given.

Transmissions of NO2 together with H2O and CO2 in the spectral region 1627–1637 cm−1 for the power setting NH of 65%. The absorption signatures for single pass (total transmission) as well as for 16 and 32 passes are given.

Optical depths of NO and interfering compounds (CO2 and H2O) in the spectral region 1895–1905 cm−1 for the power setting NH of 65%. The absorption signatures for 32 passes of single gases as well as of the gas mixture (sum) are given.

Transmissions of NO together with H2O and CO2 in the spectral region 1895–1905 cm−1 for the power setting NH of 65%. The absorption signatures for single pass (total transmission) as well as for 32 passes are given.

Comparison of the background spectrum collected by the FTIR spectrometer (given in millivolts, i.e., arbitrary units) without acoustic noise (top) and with a noise level of 100 dB (bottom) in a frequency range from 200 to 400 Hz.

Inversion results of intrusive measurements and measurements taken with the Kriesche system for a CO mixing ratio across the plume versus the distance to the plume axis at 91% NH (takeoff turbine conditions).

Inversion results of intrusive measurements and measurements taken with the Kriesche system for a NO mixing ratio across the plume versus the distance to the plume axis at 91% NH (takeoff turbine conditions).

aq is the peak column density in the line of sight perpendicular to the plume at the plume axis with a peak mixing ratio C. Q is the total column density across the whole plume profile in this line of sight: Gaussian H2O profile with shoulder, NO and NO2 mixing ratio profiles calculated from Gaussian H2O profiles with a shoulder by use of different peak values of the mixing ratio and consequently of the column density and total column density.

a Calculated under the assumption of a signal-to-noise-ratio of 2 to 1 and 20 times higher noise in the spectra measured in the turbine exhaust gas.b Detection limit estimated by taking into account a higher sensitivity of the detector at a lower resolution.

aq is the peak column density in the line of sight perpendicular to the plume at the plume axis with a peak mixing ratio C. Q is the total column density across the whole plume profile in this line of sight: Gaussian H2O profile with shoulder, NO and NO2 mixing ratio profiles calculated from Gaussian H2O profiles with a shoulder by use of different peak values of the mixing ratio and consequently of the column density and total column density.

a Calculated under the assumption of a signal-to-noise-ratio of 2 to 1 and 20 times higher noise in the spectra measured in the turbine exhaust gas.b Detection limit estimated by taking into account a higher sensitivity of the detector at a lower resolution.